The present invention relates to a display device that is advantageously used as an automobile indicator lamp and in other applications. More specifically, the present invention relates to an improved display device that allows its display portion to be illuminated with light of varying colors.
A prior art display device that allows the display portion of a display panel to be illuminated with light from a light source is shown in FIG. 1. This display device, generally indicated at 1, is used as an automobile indicator lamp. Its basic components are a light source 2, a case 3 for accommodating the light source 2, and an optically translucent (light-transmitting) display panel 4 that closes the front opening of the case 3. A light-shielding film 6 is formed on the entire surface of the back side of the display panel 4 except for the area corresponding to display portion 5. One application of this display device is its use as an oil indicator; if the residual amount of oil falls below a given level, the light source 2 is lit and illuminates the display portion 5 to inform the driver of the fact that the oil will run out soon. In this type of display device, the quantity of light that is transmitted through the display portion is always constant. However, the ambient brightness differs considerably between daytime and nighttime and the driver wants different colors of illumination to be provided as necessity arises.
In order to meet this demand, it is desirable that the illumination for daytime has a red or orange color whose visibility sensitivity is high enough to allow the driver to easily confirm the lighting of the lamp while in nighttime the color of illumination is changed to yellow or yellow green which causes less glare because of its low visibility sensitivity. Conventionally, this is achieved by selective use of two light sources that are covered with bulb filters 7 having different colors. However, this method is costly since it requires two light sources and associated components such as a circuit for switching from one light source to the other. In addition, the system employing this method requires complicated electrical wiring and has great potential for suffering a lot of problems.